Hearing guard and ear protector



Sept. 23, 1947. DUNBAR AL 2,427,664

HEARDIG GUARD AND EAR PROTECTOR Filed Sept. 17, 1945 Fig.

damn if Dunbar John S. Knight TAT E HEARING GUARD AND EAR PROTECTOR James Y. Dunbar and John S. Knight, United States Navy Application September 17, 1945, Serial No. 616,942

3 Claims. (Cl. 128151) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention pertains to improvements in tection when acted on by a force of pounds .per hearing guards and especially to a plug for prosquare inch. It has also been found that an tecting the inner ear and contiguous brain secincrease in weight of a lead plug from .005 pound tions from damage due to blast and shock waves, to .020 pound or an increase in weight by 4 times and from excessive sound levels. 5 will decrease the shock only about half. There- The use of hearing guards of rubber, composifore, the weight should be selected for wearing tion, wax, and cotton has long been customary comfort. in an effort to protect the ear mechanism, The Although lead is preferred as the impedance use of modern explosives has rendered these inmass, any heavy mass could be used without deadequate. Attempts have also been mad to filter lo parting from the scop of the invention. The out certain intense sounds and to seal the ears mass should be encased in a holder of rubber. against high pressures without satisfactory neoprene, or any other resilient material formed result. to fit into the outer ear canal. It should be pro- Present records and data show that damage vided with resilient sealing flange or flanges 4 to does not coincide with excess pressures or dural5 prevent irritation and provide a sn fi a tion of pressure alone. Injury in some cases is should preferably be provided with a tab 5 to pregreater even with the use of ear plugs as the rate vent too deep ear penetration as shown in Fig. 1. of pressure change is increased, even when low The mass may also be rubber mixed with a memaximum pressures are encountered. It, theretallic salt of the type shown in Fig. 2. In other fore, appears that damage is caused by the rate Words y relatively h h density t rial will of rise of pressure which is a shock function. sufiice.

An object of this invention is to provide an A small perforation or channel 3 is provided to ear plug capable of offering sufficient mass imextend through the mass designed to pass audible pedance to resist sudden pressure changes with quency and moderate intensity of peech and a minimum of exposed area and provided with being small enough to prevent high pressure or means for hearing conversation, and equalizing energy sounds from DaS gso doing the perair pressure in the outer ear canal. forated Plug acts to d p ds or noises of Details of the invention will become apparent hi frequency d l filter S u ds of high infrom a description of the following figures in n i y n pr ure. wh h; The filtering protection of the perforation or Fig. 1 is a cross section of a hearing guard and tube 3 is a function of e th and diameter of ear protector provided with a heavy mass imp pedgmce b If the air confined in the outer ear canal 6 in Fig. 2 is a cross section of an ear protector of front of the drum membrane pamlm heavy mass in which the mass of the protector 1 and the tubular op ning i the P commilhiperforms t e required impedance function; cating therewith is considered as a resonator with Fig. 3 shows the ear protector of Fig. 2 inserted a restricted neck as Shown in then, in the outer ear canal. Z

In Fig. 1 an ear protector l of any well known Natural frequency of the System fn= design is provided with a heavy mass impedance member 2, as shown. It will be noted that the M =inertence heavy mass inertia plug is perforated at 3 for a r purpose later described.

Without any protection the air in the external passage of the ear canal is compressed when acted on by a blast force resulting in acceleration of the ear drum. A heavy mass plug in the V C capacitance =density l=length of tube R=radius of tube outer ear offer impedance t0 V=chamberv01ume changes of pressure. The resistance offered by c=velocity of sound in air the mass to wave fronts of high intensity will Re R prevent injurious blast shock on the ear drum f,.= =K= and increase the efficiency of the ear protector. zl/Vl It has been found that a lead plug weighing in which K is a constant for all practical pur- .005 pound will accelerate approximately /iooo poses. as much as would the ear drum without pro- It i 61'flf016, ap nt th fr q n y Of he 

